Apparatus for treating a gas containing hydrogen sulphide and sulphur dioxide, comprising a step for depleting the recycled solvent in sulphur

ABSTRACT

An apparatus for treating a gas containing hydrogen sulphide and sulphur dioxide comprising a first gas-liquid reactor-contactor ( 2 ), means ( 3 ) for supplying a gas to be treated and means ( 5 ) for supplying an organic solvent, means ( 25 ) for recovering sulphur and means ( 20 ) for extracting a gaseous effluent containing sulphur in vapour form, the apparatus being characterized in that it comprises a second reactor-contactor ( 102 ) connected to the means for extracting the gaseous effluent, means ( 105 ) for supplying an organic solvent which is depleted in sulphur connected to the second reactor-contactor, means ( 120 ) for recovering a gaseous effluent which has been cleaned of sulphur connected to the second reactor-contactor, means ( 104 ) for extracting a liquid phase containing the organic solvent and sulphur connected to the second reactor-contactor, at least one means for depleting at least a portion of the liquid phase in sulphur connected to the means for extracting the liquid phase, comprising at least one means ( 190 ) for cooling said phase connected to a means ( 118 ) for separating solid sulphur which delivers a solid phase ( 125 ) of sulphur at a first end and a liquid phase ( 121 ) which is depleted in sulphur at a second end, the second end being connected to means ( 105 ) for supplying solvent depleted in sulphur, the apparatus being further characterized in that at least one of the reactor-contactors contains a catalyst.

This is a division of application Ser. No. 08/929,445 filed Sep. 16,1997, now U.S. Pat No. 5,935,547.

BACKGROUND OF THE INVENTION

The present invention particularly concerns an and apparatus fortreating a gaseous effluent from a Claus plant or a gas containinghydrogen sulphide and sulphur dioxide.

In particular, it concerns the treatment of effluents from Claus plantsfrom hydrodesulphurization and catalytic cracking units. It alsoconcerns the purification treatment of natural gas.

The prior art is illustrated by French patent application FR-A-2 411802.

The Claus process is widely used to recover elemental sulphur fromgaseous feeds containing hydrogen sulphide (H₂S). However, the fumesemitted from these Claus type plants, even after several catalyticstages, contain non negligible amounts of acid gases. Those effluents(tail gases) from Claus plants must, therefore, be treated to eliminatethe majority of toxic compounds so as to satisfy anti-pollutionregulations. These regulations are becoming more and more strict andexisting technology must be constantly improved.

As an example, about 95% by weight of the sulphur present can berecovered from a Claus plant; treatment of this Claus plant tail gas(using a Clauspol unit, for example) can recover 99.8% by weight of thesulphur, for example, using the reaction:

2H₂S+SO₂3S+2H₂O

which uses a reaction medium constituted by an organic solvent and acatalyst comprising an alkaline or alkaline-earth salt of an organicacid. The reaction is generally carried out in counter-current mode in areactor-contactor and its temperature is controlled by passing thesolvent which is extracted from the lower end of the reactor by acirculating pump through a heat exchanger to encourage the highestpossible degree of conversion to sulphur while avoiding the formation ofsolid sulphur. Sulphur is thus recovered in liquid form. While it isvery effective, the process is limited by various constraints:

The thermodynamic equilibrium of the reaction is such that the reactionis never complete. Some hydrogen sulphide and sulphur dioxide remains,in equilibrium with the sulphur and water which are formed. The quantityof sulphur present in unreacted H₂S and SO₂ which is found in thereaction effluent (from the Clauspol) corresponds to about 0.1% of thetotal sulphur in the initial feed to the Claus plant. Better conversioncan be envisaged at a lower operating temperature but this temperaturemust be kept above the freezing point of sulphur (about 120° C.)otherwise the reactor will be blocked with solid sulphur;

The presence of unseparated liquid sulphur in the reactor-contactor,which is entrained in the solvent and catalyst which circulate, andwhich is recycled to the reactor-contactor. Not all of the droplets ofliquid sulphur are separated from the solvent and the presence of liquidsulphur irremediably causes the presence of gaseous sulphur in theeffluent due to the vapour pressure of sulphur. As an example, thequantity of unrecovered sulphur which can be attributed to vapourpressure is about 0.1% by weight of the sulphur in the initial feed.

The aim of the invention is to overcome the disadvantages of the priorart.

A further aim of the invention is to satisfy the strictest regulationsdesigned to counter atmospheric pollution by sulphur-containingcompounds.

A yet still further aim of the invention is to be able to modifyexisting installations with a Claus plant and a unit for treating theeffluents from that unit (a Clauspol unit), at very low cost.

It has been shown that by eliminating all of the sulphur vapour from theeffluents from gas treatment units, for example Claus plant tail gas, upto 99.9% of the total sulphur can be recovered and thus the quantity ofsulphur discharged into the atmosphere when the gas is incinerated canbe minimised.

More precisely, as aspect of the invention concerns a process for thetreatment of a gas containing hydrogen sulphide and sulphur dioxide, inwhich the gas is brought into contact with an organic solvent containinga catalyst in at least one gas-liquid reactor-contactor at a suitabletemperature, and a gaseous effluent which substantially no longercontains hydrogen sulphide and sulphur dioxide but which containssulphur in vapour form is recovered, the process being characterized inthat the gaseous effluent from the reactor-contactor is brought intocontact with the same organic solvent or with another organic solvent ata temperature which is lower than the solidification temperature ofsulphur (for example 95° C.) in a contactor-cooler.

We have observed that bringing an organic solvent which is partiallydepleted in sulphur into contact with a gaseous feed from which aportion of the H₂S and SO₂ has been removed has produced very goodresults.

In more detail, in the process for the treatment of a gas containinghydrogen sulphide and sulphur dioxide the gas (3) is brought intocontact with at least one organic solvent in a first gas-liquid contactand reaction zone at a suitable temperature and an effluent containingwater and sulphur vapour is recovered separately from an effluentcontaining sulphur, the process being characterized in that the gaseouseffluent is introduced into a second contact zone, and brought intocontact under suitable conditions with at least one recycled organicsolvent which is depleted in sulphur, a purified gas substantially nolonger containing sulphur vapour is recovered separately from saidsolvent which is rich in sulphur, at least a portion of saidsulphur-rich solvent is removed, advantageously at most 50% of the flow,said portion of solvent is cooled to obtain a suspension of sulphurcrystals in the solvent, the sulphur crystals are separated from thesolvent and said portion of cooled solvent which is depleted in sulphuris recycled at least in part to the second contact zone, the processbeing further characterized in that at least one of the two contactzones contains at least one catalyst.

In accordance with one characteristic of the process aspect invention,the remaining portion of the sulphur-rich organic solvent from thesecond contact zone is recycled to the second contact zone, moreprecisely to its upper portion, after optional cooling.

In a further characteristic of the process, the portion of solvent whichis to be depleted in sulphur is cooled by indirect heat exchange or bymixing with a suitable quantity of water or by a combination of thesemeans at a temperature which is generally less than the meltingtemperature of sulphur, preferably at a temperature which is in therange 40° C. to 110° C. The quantity of water which is advantageouslyintroduced is such that a solvent/water mixture containing 30% to 70% byweight of water is obtained.

The sulphur depletion operation consists of removing at least a portionof the sulphur-enriched organic solvent, generally at most 50% of theflow leaving the second contact zone and preferably 2% to 10% of theflow of liquid phase, and cooling it to a temperature such that asuspension of sulphur crystals is obtained in the solvent saturated insulphur at said cooling temperature. After separating the sulphurcrystals, the solvent which is depleted in sulphur with respect to thatpresent in the second reactor-contactor can be re-heated to thetemperature of the second reactor-contactor before being introduced intoit.

At least a portion of a single-phase solution of said organic solventcan be extracted from the lower portion of the first contact zone,cooled to eliminate at least a portion of the heat of reaction released,then recycled to the first contact zone.

The temperature of the second contact zone is advantageously less thanthat of the first zone, preferably by 15° C. to 20° C.

It is of great advantage to use the same organic solvent in the firstand in the second contact zones. In this case, a solvent line can beconnected between the means for recycling the single-phase solution withreduced temperature from the first reactor, and the inlet to the heatexchanger cooling at least a portion of the sulphur-enriched solvent.This line acts as the line for adding solvent to the secondreactor-contactor.

The catalyst is preferably introduced into the first reactor-contactor.Thus the majority of the sulphur present in the form of H₂S and SO₂ andcontained in the gas to be treated is eliminated, the second reactoronly providing a finishing treatment which reduces the dimensions of theequipment. Clearly, it can be introduced into the secondreactor-contactor alone, or into both.

For vertical reactors, there are two variations of the process of theinvention.

In a first variation, both the gas and organic solvent in the firstcontact zone and the gaseous effluent and organic solvent in the secondcontact zone are brought into contact in co-current mode, the gas supplyor the gaseous effluent supply being made to the upper portion of thecontact zones along with the organic solvent supply.

In a second, preferred, variation, both the gas and organic solvent inthe first contact zone and the gaseous effluent and organic solvent inthe second contact zone are brought into contact in counter-currentmode, the gas supply or the gaseous effluent supply being made to thelower portion of the contact zones and the organic solvent supply beingmade to the upper portion of the contact zones.

Clearly, the process can also be carried out in horizontal reactors.

SUMMARY OF THE INVENTION

The invention also concerns an apparatus for treating a gas containinghydrogen sulphide and sulphur dioxide. It normally comprises a firstgas-liquid reactor-contactor (2), means (3) for supplying a gas to betreated and means (5) for supplying an organic solvent, means (25) forrecovering sulphur and means (20) for extracting a gaseous effluentcontaining sulphur in vapour form, the apparatus being characterized inthat it comprises a second reactor-contactor (102) connected to themeans for extracting the gaseous effluent, means (105) for supplying anorganic solvent which is depleted in sulphur connected to the secondreactor-contactor, means (120) for recovering a gaseous effluent whichhas been cleaned of sulphur connected to the second reactor-contactor,means (104) for extracting a liquid phase containing the organic solventand sulphur connected to the second reactor-contactor, at least onemeans for depleting at least a portion of the liquid phase in sulphurconnected to the means for extracting the liquid phase, comprising atleast one means (190) for cooling said phase connected to a means (118)for separating solid sulphur which delivers a solid phase (125) ofsulphur at a first end and a liquid phase (121) which is depleted insulphur at a second end, the second end being connected to the means(105) for supplying solvent depleted in sulphur, the apparatus beingfurther characterized in that at least one of the reactor-contactorscontains a catalyst.

When only a portion of the liquid phase containing the organic solventand sulphur from the second reactor-contactor is cooled to eliminatesulphur, a line connected to the means for extracting said liquid phasecan be connected to the means for supplying solvent depleted in sulphurof the second reactor-contactor to recycle the remaining portion of theliquid phase.

It may be of advantage to combine the first reactor-contactor and thesecond reactor-contactor in the same vessel. However, these tworeactor-contactors can be separate.

This is particularly the case when the second reactor-contactorcomprises a venturi scrubber type mixer-contactor combined with aseparator for separating purified gaseous effluent from the liquidphase, wherein the extraction line is connected to the sulphur depletionmeans.

The organic solvent can be cooled in different manners:

In a first variation, if the organic solvent is miscible with water, itcan be cooled by heat exchange in a heat exchanger before being mixedwith the gaseous effluent to be purified, by adding water at atemperature which is lower than that of the organic solvent, wherein theheat of vaporisation on contact with the gaseous effluent can reduce thetemperature of the mixture, or by a combination of the above two steps.Cooling is preferably by injection of water.

In a second variation, if the organic solvent is not miscible withwater, it can be cooled in the same manner as in the first variation.Cooling is preferably by heat exchange.

The following different types of solvents can be used:

In the category of solvents which are insoluble in water arehydrocarbons with boiling points at atmospheric pressure of more than200° C., preferably dodecane, tridecane, and naphtha with boiling pointsin the range 225° C. to 335° C.

In the category of solvents which are soluble in water, with boilingpoints at atmospheric pressure of more than 200° C. are polyolscontaining 2 to 15 carbon atoms, preferably glycerol, thiodiglycol andcyclohexanedimethylethanol, acid esters containing 5 to 15 carbon atoms,more particularly trimethylpentanediol mono-isobutyrate and dimethyladipate, glycol ethers containing 5 to 15 carbon atoms, advantageouslybutoxytriglycol, ethoxytriglycol, diethylene glycol butylether, ethyleneglycol phenylether, terpinyl ethylene glycol monobenzyl ether, ethyleneglycol butylphenylether, diethylene glycol, diethylene glycoldimethylether, diethylene glycol dibutylether, triethylene glycol,tetraethylene glycol dimethylether, propylene n-butylether, dipropylenen-butylether, tripropylene n-butylether, and polyethylene glycol with amolar mass of 200, 300, 400 or 600.

The catalysts and solvents which are generally used are those described,for example, in French patents FR-A-2 115 721 (U.S. Pat. No. 3,796,796),FR-A-2 122 674 and FR-A-2 138 371 (U.S. Pat. No. 3,832,454) which arehereby incorporated by reference. More particularly, alkaline salts oforganic acids such as benzoic acid and salicylic acid can be used ascatalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will better understood from the following drawings whichschematically illustrate a prior art apparatus (FIG. 1) and twovariations of an apparatus, in which:

FIG. 1 shows a prior art apparatus;

FIG. 2 shows two separate reactor-contactors; and

FIG. 3 shows two reactor-contactors in the same vessel.

In FIG. 1, the lower portion of a vertical reactor-contactor (2)receives a gas containing H₂S and SO₂ via a supply line (3). Thisreactor comprises a column (2) containing a packing bed (2 a) of Intaloxsaddles, for example, which are capable of retaining the sodium saltsformed during the reaction. An organic solvent containing a solublecatalyst supplied via line (1) and originating from a recycle line (4)at the lower portion of reactor-contactor (2) is introduced via a line(5) to the upper portion of the reactor so that the gas to be treatedcontacts the solvent in counter-current mode. The solvent of line (4) iscooled by a heat exchanger (19) the temperature of which is monitoredand regulated by a measuring system (30) associated with a valve (31)located in a line (32) for introducing hot water at about 80° C. Thiswater is evacuated via a line (32 a).

Purified gas is extracted overhead from the reactor via a line (20)while the sulphur formed settles to the bottom of the reactor and isextracted via a line (25).

In FIG. 2 which shows one embodiment of an apparatus of the invention,the apparatus comprises two separate vertical reactor-contactors, thefirst of which is as the description of FIG. 1 with the same referencenumerals.

Line (20) recovering the gaseous effluent from the firstreactor-contactor (2) supplies the lower portion of a secondreactor-contactor (102) comprising a packing bed (102 a) which may ormay not be identical to the first reactor.

Catalyst supplied via line (101) and organic solvent are introduced vialines (104), (104 a) and (105) to the head of the secondreactor-contactor which thus carries out gas-liquid contact in thepacking in counter-current mode.

A portion, 2% to 10%, for example, of the solvent containing sulphur andcatalyst extracted via line (104) is cooled to 60-70° C. by an indirectheat exchanger (190) via a line (116), which crystallises the sulphurand depletes the solvent in sulphur. Heat exchange is effected byinjecting water (132) and evacuating (132 a) water on a line (121)upstream of an exchanger (121 a).

The suspended sulphur is sent to a hydrocyclone (118) where the solventis separated from the sulphur. At the head of the hydrocyclone, a line(121) on which a further heat exchanger (121 a) can optionally belocated to reheat the sulphur-depleted solvent, is connected to line(104 a), which is also optionally cooled, and their contents arerecycled via line (105) above the packing (102 a).

A cooling control valve (131) connected to exchanger (190) is associatedwith a temperature control (130) connected to a temperature probelocated upstream of exchanger (121 a) in line (121).

Sulphur is recovered from the bottom of hydrocyclone (118) via line(125) and mixed with that from the first reactor-contactor (2) andmelted before being extracted via line (25).

Finally, the purified gas is recovered from the head of the secondreactor-contactor via a line (120).

When the organic solvent and the catalyst are the same in both reactors,a line (5 a) connected to line (5) of the first reactor-contactor canadd solvent and catalyst to the second, introducing it to the inlet toexchanger (190).

Clearly, when the solvents in the two reactors are different, this line(5 a) is dispensed with and sulphur from hydrocyclone (118) is producedand melted separately via line (125).

In FIG. 3, a vertical reactor-contactor composed of two reaction andcontact stages (2 and 102) form the first and second reactor-contactorsof FIG. 2, with the exception that:

the first reactor-contactor does not contain catalyst and thus has nocatalyst supply line (1) in the solvent line (4);

the gas, partially freed of H₂S and SO₂ is introduced directly into thelower portion of the second step (102) by line or chimney (20) whichalso recovers solvent, catalyst and sulphur extracted via line (104) tobe partially depleted in sulphur by exchanger (190) and hydrocyclone(118).

The following examples illustrate the invention:

EXAMPLE 1

Prior Art (FIG. 1)

The characteristics were as follows:

Feed: Claus plant tail gas, flow rate: 12302 Nm³/h;

Reactor temperature: 125° C.;

Packing: ceramic Intalox saddles, specific surface area: 250 m²/m³;

Solvent: Polyethylene glycol, MW=400, flow rate: 500 m³/h;

Catalyst: sodium salicylate, concentration 100 millimoles per kg ofsolvent;

Recycled solvent (lines 4 and 5):

Flow rate: 500 m³/h;

Temperature: 123° C.;

Flow rate of sulphur produced (line 25): 315 kg/h.

The compositions of the inlet and outlet gases to and from the plant areshown in Table I below:

TABLE I Inlet gas (3) Outlet gas (20) vol % vol % H₂S 1.234 0.126 SO₂0.617 0.063 CO₂ 4.000 4.072 COS 0.015 0.009 CS₂ 0.015 0.009 S_(V)* 0.1400.031 N₂ 60.000 61.079 H₂O 34.000 34.612 Sum of sulphur- 2.036 0.247containing compounds *S_(V) = sulphur vapour + vesicular sulphur.

The yield of sulphur-containing compounds in the reactor was:${\frac{\begin{matrix}\left( {{\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {inlet}} -} \right. \\\left. {\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {outlet}} \right)\end{matrix}}{\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {inlet}} \times 100} = {{\frac{\left( {2.036 - 0.247} \right)}{2.036} \times 100} = {88\%}}$

The Claus plant had a yield of 94%

The yield of the Claus plant assembly+finishing unit was:

94+(6×0.88)=99.28

EXAMPLE 2

In Accordance with the Invention (FIG. 2)

The feed, organic solvent, catalyst and packing were those of Example 1.

The operating conditions for the first reactor-contactor (2) were thesame as for Example 1.

The relative conditions for the second reactor-contactor (102) were asfollows:

Temperature: 110° C.;

Flow rate of solvent and sulphur (line 104): 500 m³/h;

Flow rate of cooled solvent (line 116): 50 m³/h;

Temperature of cooled solvent: 65° C.;

Temperature of recycled solvent: (line 105): 108° C.;

Recovered sulphur (line 25): 344.3 kg/h.

The compositions of the inlet gas (line 3) and outlet gas to and fromthe plant are shown in Table II below:

TABLE II Inlet gas (3) Outlet gas (20) vol % vol % H₂S 1.234 0.040 SO₂0.617 0.020 CO₂ 4.000 4.084 COS 0.015 0.009 CS₂ 0.015 0.009 S_(V)* 0.1400.003 N₂ 59.990 61.180 H₂O 33.990 34.670 Sum of sulphur- 2.032 0.090containing compounds *S_(V) = sulphur vapour + vesicular sulphur.

The yield of sulphur-containing compounds in the reactor was:${\frac{\begin{matrix}\left( {{\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {inlet}} -} \right. \\\left. {\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {outlet}} \right)\end{matrix}}{\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {inlet}} \times 100} = {{\frac{\left( {2.032 - 0.090} \right)}{2.032} \times 100} = {95.57\%}}$

The Claus plant had a yield of 94%

The yield of the Claus plant assembly+finishing unit was:${94 + \frac{\left( {6 \times 95.57} \right)}{100}} = 99.73$

EXAMPLE III

In Accordance with the Invention (FIG. 3)

A vertical reactor-contactor composed of two stages through which thegas to be treated passed successively:

Lower Stage (2)

The conditions were similar to those of the reactor of Example 1; thegas flow conditions and the composition of the gas to be treated werethe same.

However, no catalyst was used in this step.

Upper Stage (102)

The operating conditions were strictly the same as those of the reactor(102) of example 2. All of the catalyst was introduced via line (101).

The compositions of the inlet gas (line 3) and outlet gas (line 120) toand from the plant are shown in Table III below:

TABLE III Inlet gas (3) Outlet gas (20) vol % vol % H₂S 1.234 0.063 SO₂0.617 0.0315 CO₂ 4.000 4.000 COS 0.015 0.006 CS₂ 0.015 0.006 S_(V)*0.140 0.004 N₂ 60.000 60.000 H₂O 34.000 34.000 Sum of sulphur- 2.0360.1165 containing compounds *S_(V) = sulphur vapour + vesicular sulphur.

The yield of sulphur-containing compounds in the reactor was:${\frac{\begin{matrix}\left( {{\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {inlet}} -} \right. \\\left. {\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {outlet}} \right)\end{matrix}}{\% \quad {of}\quad {sulphur}\text{-}{containing}\quad {compounds}\quad {at}\quad {inlet}} \times 100} = {{\frac{\left( {2.036 - 0.1165} \right)}{2.036} \times 100} = {94.27\%}}$

The Claus plant had a yield of 94%.

The yield of the Claus plant assembly+finishing unit was:${94 + \frac{\left( {6 \times 94.27} \right)}{100}} = 99.65$

What is claimed is:
 1. An apparatus for treating a gas containinghydrogen sulphide and sulphur dioxide comprising a first gas-liquidreactor-contactor (2), means (3) for supplying a gas to be treated intothe first reactor-contactor and means (5) for supplying an organicsolvent into the first reactor-contactor, means (25) for recoveringsulphur from the first reactor-contactor and means (20) for extracting agaseous effluent containing sulphur in vapour form from the firstreactor-contactor, a second reactor-contactor (102) connected to themeans (20) for extracting the gaseous effluent, means (105) forsupplying an organic solvent which is depleted in sulphur connected tothe second reactor-contactor, means (120) for recovering a gaseouseffluent which has been cleaned of sulphur connected to the secondreactor-contactor, means (104) for extracting a liquid phase containingthe organic solvent and sulphur connected to the secondreactor-contactor, at least one means for depleting at least a portionof the liquid phase in sulphur connected to the means (104) forextracting the liquid phase, said means for depleting comprising atleast one means (190) for cooling said liquid phase connected to a means(118) for separating solid sulphur which delivers a solid phase (125) ofsulphur at a first end and a liquid phase (121) which is depleted insulphur at a second end, the second end being connected to means (105)for supplying solvent depleted in sulphur, wherein at least one of thereactor-contactors contains a catalyst.
 2. An apparatus according toclaim 1, in which a line (104 a) connected to the means (104) forextracting the liquid phase containing the organic solvent and sulphuris connected to means (105) for supplying organic solvent which isdepleted in sulphur.
 3. An apparatus according to claim 1, in which thecooling means (190) is selected from the group formed by a heatexchanger, water addition and a combination of the two.
 4. An apparatusaccording to claim 1, in which the first reactor-contactor (2) comprisesat its lower side means (4) for extracting a single-phase solution,means (30) for monitoring and controlling the temperature of thesolution associated with a heat exchanger (19) and connected to thesolution extraction means (4) and means (5) for recycling thesingle-phase cooled solution to the first reactor-contactor.
 5. Anapparatus according to claim 1 in which the first reactor-contactor (2)and the second reactor-contactor (102) are contained in the same vessel.6. An apparatus according to claim 1 in which the secondreactor-contactor comprises a venturi-scrubber type mixer-contactorassociated with a separator for separating purified gaseous effluentfrom the liquid phase.
 7. An apparatus according to claim 1, in which aline (5 a) is connected between the means (5) for recycling thesingle-phase solution from the first reactor-contactor to the firstreactor-contactor, which has been cooled, to the inlet of the liquidphase cooling means (190).
 8. An apparatus according to claim 2, inwhich the first reactor-contactor (2) comprises at its lower side means(4) for extracting a single-phase solution, means (30) for monitoringand controlling the temperature of the solution associated with a heatexchanger (19) and connected to the solution extraction means (4) andmeans (5) for recycling the single-phase cooled solution to the firstreactor-contactor.
 9. An apparatus according to claim 4, in which thefirst reactor-contactor (2) and the second reactor-contactor (102) arecontained in the same vessel.
 10. An apparatus according to claim 8, inwhich the first reactor-contactor (2) and the second reactor-contactor(102) are contained in the same vessel.
 11. An apparatus according toclaim 2, in which a line (5 a) is connected between the means (5) forrecycling the single-phase solution from the first reactor-contactor tothe first reactor-contactor, which has been cooled, to the inlet of theliquid phase cooling means (190).
 12. An apparatus according to claim 4,in which a line (5 a) is connected between the means (5) for recyclingthe single-phase solution from the first reactor-contactor to the firstreactor-contactor, which has been cooled, to the inlet of the liquidphase cooling means (190).
 13. An apparatus according to claim 6, inwhich a line (5 a) is connected between the means (5) for recycling thesingle-phase solution from the first reactor-contactor to the firstreactor-contactor, which has been cooled, to the inlet of the liquidphase cooling means (190).
 14. An apparatus according to claim 8, inwhich a line (5 a) is connected between the means (5) for recycling thesingle-phase solution from the first reactor-contactor to the firstreactor-contactor, which has been cooled, to the inlet of the liquidphase cooling means (190).
 15. An apparatus according to claim 9, inwhich a line (5 a) is connected between the means (5) for recycling thesingle-phase solution from the first reactor-contactor to the firstreactor-contactor, which has been cooled, to the inlet of the liquidphase cooling means (190).
 16. An apparatus according to claim 10, inwhich a line (5 a) is connected between the means (5) for recycling thesingle-phase solution from the first reactor-contactor to the firstreactor-contactor, which has been cooled, to the inlet of the liquidphase cooling means (190).